It is already known to use probes for carrying out measurement, analyses or samplings in blast furnaces. Such probes are generally tubular, or at least comprise a tubular part at their end in order to be able to receive the measuring means or to make the required samplings.
In the case of gas samplings or pressure measurements, for example, these probes can advantageously be permanently closed off at their end and have only an orifice large enough for the gases to flow through. This orifice is preferably situated on the lateral wall close to the end of the probe nose. This particular disposition reduces the risks of said orifice being accidentally damaged by the solid or liquid materials when the probe is introduced into the furnace.
If, on the contrary, such a probe is used for sampling non-gaseous materials or for example for measuring the temperature with a radiation pyrometer, situated inside the probe, it is important for the end of the probe to be free. Yet, if a tubular probe, with an open end, is introduced in a smelting furnace, hence a furnace containing high temperature materials, there is a risk for the nose of the probe to become choked up, or for the instruments inside the probe to become damaged, for example through contact with noxious or corrosive gases or through excessive temperatures.
In order to solve this problem, it has already been proposed to temporarily close off the probe nose with a plug, which is removable or ejectable by suitable means or methods when the probe nose has reached the target area. These plugs of course are not recoverable since they are ejected inside the furnace.
French Patent Application No. 2 472 018 filed by Nippon Steel Corp. describes probes equipped with such plugs. This document describes plugs which are inserted in the nose of the probe and which are removed by frictional contact with the material inside the furnace during a movement of retraction of the probe when said probe has penetrated beyond the area to be probed. This method is not completely reliable in that the plug, being removable, risks to fall off accidentally when the probe is introduced in the furnace, and this must be avoided. In reverse, if the plug is very tightly fitted in the nose, precisely to avoid accidental ejection therefrom, then such ejection may not occur at the exact spot.
It may also be necessary to protect the measuring instruments contained in the probe against the high temperatures and against possible pollution from the gases penetrating into the probe through inadequate tightness between the plug and the probe nose. To this effect, it is proposed to inject a neutral gas, such as nitrogen, inside the probe, under a certain pressure.
However, as the gas pressure inside the blast furnace in which the probe is introduced, is not necessarily known with precision, especially as it can vary, for example during the probe introduction time, the plug risks falling off under an excessive difference between the pressure of the gas inside the probe and the pressure inside the furnace.
The problem arising then is that of adapting the pressure of the gas injected into the probe, to the pressure inside the furnace, in order to avoid, first the infiltering into the probe of gases issued from the furnace, and second, the untimely ejection of the plug.